Significant PK variability of plasma-derived FIX concentrates in chinese children with Haemophilia B: A fixed single-dose study of factor IX-CTBB.

Abstract

Background: The pharmacokinetics (PK) characters of plasma-derived Factor IX (pdFIX) concentrate in Chinese children with Haemophilia B(HB) have not yet been reported.

Aim: To assess the PK parameters of pdFIX in children with severe HB and identify factors that influence FIX PK.

Methods: This non-randomized, open-label PK study enrolled children with severe HB (FIX≤2 %). Patients received 50 IU± 5 IU/kg pdFIX (Human coagulation Factor IX-CTBB) after at least 96 h wash-out period. Blood samples for PK assessments were collected before infusion (pre-dose) and at 15 min, 30 min, 1 h, 3 h, 6 h, 9 h, 24 h, 48 h, 72 h and 96 h post-infusion. FIX activity was measured by a one-stage assay.

Results: Twenty patients were enrolled with a median age of 8.3 (range 1.8-15.4) years. The peak plasma levels of FIX: C in all patients were observed within 15 min. Their median terminal half-life (t_1/2) was 32.6 (range 23.3-52.0) hours. The median values of in vivo recovery (IVR) at 15 min, clearance (CL), volume of distribution at state (Vss) and area under the curve (AUC) were 1.0 (0.9, 1.2) IU/dL per IU/kg, 5.2 (IQR 4.8, 6.4) mL/h/kg, 207.9 (IQR 183.5, 301.4) mL/kg, 9.77 (IQR 7.76, 11.23) U*h/mL respectively. The t_1/2, Vss and mean residence time after intravenous injection (MRT) decreased with increasing age and body weight. Changes in CL with body weight were similar to t_1/2, but no significant correlation exists with age.

Conclusions: There is a significant inter-individual variability in PK profiles among Chinese children with severe HB, which is related to age and body weight changes, indicating the necessity of individualized prophylaxis driven by PK.